A variety of keyless chucks have been developed so far. A conventional chuck generally comprises a rear sleeve, a body, a bearing ring, a bearing, a nut, a jaw, a front sleeve, a stopper and so one. The jaw extends/retracts under the rotation of the nut and the engagement of conical threads, and the nut is rotated by movement of the front sleeve. Such a chuck is keyless if the front sleeve is rotated by hand. The chuck may be attached to a driving shaft of a drill by means of threads or a conical bore.
A conventional keyed or keyless chuck has the disadvantage that because the nut and the jaw are secured only by rotation of threads, the jaw tends to loosen its grip on a tool due to axial percussive vibrations transmitted through the chuck and the tool during operation. This will cause the tool to skid, thus resulting in a loss of working efficiency and a loss of safety.
A conventional chuck is disclosed in Chinese Patent Publication CN1068532 (Chinese Patent Number: ZL 92104999.4), in which the anti-percussion of the chuck is achieved by forming spokewise grooves in the surfaces of two members that act as bearing races, the opposing sides of the grooves being provided with round angles of different radii. The depth of the grooves has a great influence on the anti-percussion ability of the chuck as well as on the release of the chuck. If the grooves are too deep, the chuck will not be released after use. If the grooves are too shallow, the chuck will have a poor anti-percussion performance. Therefore, in order to keep a uniform depth of the grooves in all members to thereby ensure the anti-percussion ability of all chucks, it is necessary to frequently adjust the machine for manufacturing the members. This, however, will affect the efficiency of production and can result in an increase of defective products. To overcome this drawback, it is necessary to provide a pressing machine with a higher pressing accuracy or larger tonnage, which however will increase the cost of production.
Furthermore, the front sleeve of a conventional keyless chuck is generally made of plastic. The chuck generally has a configuration in which a steel ring is embedded in an inner side of the plastic front sleeve, and two nut halves that are placed in a circular groove in the body of the chuck are press-fit into the hole of the steel ring embedded in the inner side of the plastic front sleeve, thereby securing the two nut halves in the circular groove in the body. This configuration, however, is complicated in structure and manufacturing process, and the front sleeve of the chuck which has a low strength is susceptible in damage.